rotor

Abstract

To provide a technology related to rotor configuration to suppress loss due to reduction of flux linkage.SOLUTION: A rotor includes a shaft having a rotating axis, a rotor core that surrounds the shaft, four plate-shaped magnets placed on the outer surface of the rotor core, and a covering member that covers the rotor core and the magnet. When the thickness of the magnet along the radial direction of the shaft is t, and the width of the magnet along the circumferential direction of the shaft is w, the relationship t / w=0.23±0.01 is satisfied.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a rotor. [Background technology]

[0002] Patent Document 1 discloses a rotor for use in an electric motor. The rotor includes a shaft, a rotor core surrounding the shaft, and four plate-shaped magnets arranged on the outer surface of the rotor core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-81776 Summary of the Invention [Problem to be solved by the invention]

[0004] In an electric motor, a rotor rotates by sequentially passing current through multiple coils arranged circumferentially to change the magnetic field. At this time, magnetic flux generated from the magnet passes through the teeth around which the coils are wound. However, some of the magnetic flux may leak out without passing through the teeth (i.e., without contributing to the operation of the motor). This can reduce the effective magnetic flux (flux linkage) and increase energy loss. This specification provides technology related to a rotor configuration that suppresses energy loss due to reduced flux linkage. [Means for solving the problem]

[0005] The rotor disclosed in this specification includes a shaft having a rotation axis, a rotor core covering the periphery of the shaft, four plate-shaped magnets arranged on the outer surface of the rotor core, and a covering member covering the rotor core and the magnets. When the thickness of the magnets along the radial direction of the shaft is t and the width of the magnets along the circumferential direction of the shaft is w, the relationship t / w = 0.23 ± 0.01 is satisfied.

[0006] The inventors discovered that the flux linkage is maximized when the relationship between the magnet's thickness t and width w satisfies the above relationship. Therefore, the rotor described above suppresses energy loss due to reduced flux linkage, enabling the motor to operate with high efficiency.

[0007] The rotor core may have a substantially polygonal cross section perpendicular to the rotation axis, the cross section having at least a first pair of parallel sides and a second pair of parallel sides perpendicular to the first pair of sides. The magnets may be disposed on the outer surfaces of the first pair of sides and the second pair of sides. The centers of the four magnets in the width direction may overlap the midpoints of the first pair of sides and the second pair of sides, respectively. When manufacturing a rotor, limitations are imposed on the dimensions of the magnets to ensure the outer diameter of the rotor and the thickness of the covering member. In the above configuration, by arranging the centers of the magnets in the width direction to overlap the midpoints of the first pair of sides or the second pair of sides, the volume of the magnets can be maximized within a limited space.

[0008] In this specification, the term "substantially polygonal" is not limited to a shape in which the connecting portion of two sides forms a corner, but also includes a shape in which two sides are connected by a curved surface (i.e., a polygon with rounded corners). Furthermore, the term "polygonal" is not limited to a shape in which the connecting portion of two sides has a convex shape, but also includes a so-called concave polygon. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a vertical cross-sectional view showing the schematic configuration of a fuel pump. [Figure 2] 2 is a cross-sectional view showing the rotor and the stator taken along line II-II in FIG. 1; [Figure 3] FIG. 3 is an exploded perspective view showing a configuration of a part of the rotor. [Figure 4] FIG. 3 is an enlarged cross-sectional view of a portion of FIG. 2. [Figure 5] 10A and 10B are diagrams showing various variations in the shape of the magnet in a rotor having a predetermined restricted outer diameter. [Figure 6] 10A and 10B are diagrams showing various variations in the shape of the magnets in a rotor having another predetermined outer diameter constraint. [Figure 7] 10A and 10B are diagrams showing various variations in the shape of the magnets in a rotor having another predetermined outer diameter constraint. [Figure 8] 8 is a graph showing the relationship between the shape of the magnet and the no-load rotation speed in a motor using the rotor shown in FIGS. 5 to 7. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Fuel pump configuration) 1, a fuel pump 10 will be described. The fuel pump 10 is disposed in a fuel tank mounted on a vehicle such as an automobile. The fuel pump 10 includes a motor unit 20 and a pump unit 40.

[0011] The pump section 40 is disposed at the lower end of the fuel pump 10. The pump section 40 includes a casing 42 and an impeller 46. The casing 42 includes a space that houses the impeller 46 and an intake port 44 that communicates with the space. The impeller 46 is housed in the space within the casing 42 so as to be able to rotate freely.

[0012] The motor section 20 is disposed above the pump section 40. The motor section 20 is a three-phase (U-phase, V-phase, W-phase) motor. The motor section 20 is a brushless motor. The motor section 20 includes a stator 30 and a rotor 50. The stator 30 includes a stator core 32, six coils 38, a resin layer 39, and terminals 37. As shown in FIG. 2, the stator core 32 includes a yoke 34 and six teeth 36. The yoke 34 has a cylindrical shape that forms the outer circumferential surface of the stator 30. Each tooth 36 protrudes from the inner circumferential surface of the yoke 34 toward the central axis CL of the cylindrical shape of the yoke 34. The tip of each tooth 36 (i.e., the end opposite the yoke 34) extends in the rotational direction of the rotor 50.

[0013] As shown in Fig. 1, six coils 38 are arranged on the stator core 32 via a resin bobbin 33. Each coil 38 is wound around a corresponding tooth 36. The coils 38 are connected to an external power supply via terminals 37. The stator 30 is covered with a resin layer 39 except for the outer peripheral surface of the stator core 32. The resin layer 39 has an outlet port 12 for discharging fuel.

[0014] (Rotor configuration) A rotor 50 is disposed inside the stator 30. As shown in FIG. 2, the rotor 50 includes a shaft 52, a rotor core 54, a magnet 56, and a covering member 58.

[0015] The shaft 52 is made of martensitic stainless steel. The shaft 52 may be made of other magnetic or non-magnetic materials. The shaft 52 has a rotation axis CL that coincides with the central axis CL, and has a cylindrical shape extending along the rotation axis CL. Since the rotation axis CL and the central axis CL coincide, both terms will be used hereinafter. The shaft 52 rotates around the rotation axis CL. As shown in FIG. 1 , the impeller 46 is fitted to the lower end of the shaft 52. The shaft 52 is rotatably supported above the impeller 46 in the casing 42 via a bearing. This allows the shaft 52 to be rotatable relative to the stator 30.

[0016] As shown in Fig. 2, a rotor core 54 is disposed around the shaft 52. When viewed in cross section as shown in Fig. 2, the rotor core 54 has a substantially square shape. That is, the cross section of the rotor core 54 is defined by a pair of parallel sides 54a and a pair of parallel sides 54b that are perpendicular to the pair of sides 54a. Sides 54a and 54b are connected by a curved surface.

[0017] A magnet 56 is disposed on each of the outer surfaces of the pair of sides 54a and the pair of sides 54b. That is, four magnets 56 are disposed on the outer surface of the rotor core 54. The magnets 56 are disposed at intervals in the circumferential direction of the shaft 52. As shown in FIG. 3, each magnet 56 has a plate shape (a rectangular parallelepiped shape). Each magnet 56 is disposed so as to extend parallel to the rotation axis CL. Each magnet 56 has a length in the direction of the rotation axis CL that is equal to that of the rotor core 54. The magnets 56 have substantially the same shape, and are disposed rotationally symmetrical with respect to the rotation axis CL.

[0018] The rotor core 54 and each magnet 56 are covered by a covering member 58. The covering member 58 has a cylindrical shape. The shaft 52 passes through the center of the covering member 58. The covering member 58 is fixed to the outer surface of the rotor core 54 and the outer surface of each magnet 56. The central axis of the covering member 58 coincides with the rotation axis CL. The covering member 58 does not have to cover at least one of the upper and lower ends of the magnet 56. In this case, at least one of the upper and lower ends of the magnet 56 may be exposed from the covering member 58. The covering member 58 is made of, for example, resin. The rotor 50 is produced by molding the covering member 58 by placing the shaft 52, rotor core 54, and magnets 56 in a molding die, a process known as molding.

[0019] As shown in FIG. 4, when the width of the magnet along the circumferential direction of the shaft 52 is w and the thickness of the magnet along the radial direction of the shaft 52 is t, the magnet 56 is arranged so as to satisfy the relationship t / w=0.23±0.01.

[0020] Furthermore, magnet 56 is arranged so that the center position P of magnet 56 in the width direction overlaps with midpoint M of side 54a. Although not shown, other magnets 56 are also arranged so that the center positions of their width directions overlap with the midpoint of side 54a or the midpoint of side 54b.

[0021] As described above, the rotor core 54 and the magnets 56 are covered by the cylindrical covering member 58. In order to cover the entire surfaces of the rotor core 54 and the magnets 56 with the covering member 58, the outer circumferential edges of the rotor core 54 and the magnets 56 must be located more inward than the outer diameter of the rotor 50 (i.e., the outer diameter of the covering member 58), as shown in Fig. 4. In other words, the configuration of the rotor 50 has a restrictive outer diameter 60 that defines the range within which the magnets 56 can be arranged.

[0022] Therefore, as shown in Figures 5 to 8, for rotors 50 having three different types of constraint outer diameters 60, the no-load rotation speed of the motor was calculated when the thickness t and width w of the magnet 56 were variously changed, and the change in linkage magnetic flux due to the constraint outer diameter 60 and the change in linkage magnetic flux due to the shape of the magnet 56 was examined.

[0023] FIG. 5 shows various variations in the shape of the magnet in a rotor with a small constraint outer diameter 60. FIG. 6 shows various variations in the shape of the magnet in a rotor with a larger constraint outer diameter 60 than that in FIG. 5. FIG. 7 shows various variations in the shape of the magnet in a rotor with a larger constraint outer diameter 60 than that in FIGS. 5 and 6 (the constraint outer diameter 60 is approximately equal to the outer diameter of the rotor 50 (the outer diameter of the covering member 58)). In FIG. 5, the thickness t of the magnet 56 increases and the width w of the magnet 56 decreases from A1 to A8. That is, t / w increases from A1 to A8. The same is true for FIGS. 6 and 7.

[0024] FIG. 8 shows the relationship between t / w and no-load rotation speed for motors using the rotors shown in FIGS. 5 to 7. The reference symbols in the graph of FIG. 8 correspond to the reference symbols of the rotors shown in FIGS. 5 to 7. The no-load rotation speed of a motor correlates with the magnitude of the magnetic flux linkage. Specifically, the lower the no-load rotation speed of a motor, the greater the magnetic flux linkage. First, as shown in FIG. 8, it was found that the larger the constraint outer diameter 60 of the rotor 50, the lower the no-load rotation speed of the motor. The volume of the magnet 56 that can be arranged varies depending on the size of the constraint outer diameter 60. Therefore, it is thought that the larger the constraint outer diameter 60, the greater the magnetic force of the magnet 56, resulting in differences in the magnetic flux linkage. On the other hand, as shown in FIG. 8, it was found that the no-load rotation speed of a motor was minimum when t / w = 0.23, regardless of the constraint outer diameter 60. In other words, it was found that the magnetic flux linkage was maximum when t / w = 0.23, regardless of the constraint outer diameter 60.

[0025] As explained above, in this embodiment, the magnet 56 is configured so that the relationship t / w=0.23 holds between the thickness t and width w of the magnet 56. This maximizes the flux linkage of the motor and reduces energy loss.

[0026] Furthermore, as mentioned above, the larger the volume of magnet 56, the greater the flux linkage. In this embodiment, magnet 56 is positioned so that the center position P of magnet 56 in the width direction overlaps with midpoint M of side 54a. Therefore, the volume of the magnet can be secured within the restricted outer diameter 60, and the flux linkage can be maximized.

[0027] In the graph of FIG. 8, as t / w increases or decreases around t / w = 0.23, the no-load rotation speed of the motor increases (i.e., the flux linkage decreases). If t / w is too small, the distance between the magnet 56 and the teeth 36 increases at the position where the magnet 56 faces the teeth 36 of the stator 30, making it difficult for the magnetic flux to efficiently enter the teeth 36. Furthermore, as the thickness t decreases, self-demagnetization occurs, reducing the magnetic force (in other words, the magnetic flux) of the magnet 56. This is thought to result in a decrease in the flux linkage. Furthermore, if t / w is too large, the width w decreases, reducing the area of ​​the magnet 56 facing the teeth 36. In other words, the area of ​​the magnet 56 where magnetic flux is generated becomes smaller. This is thought to result in the rotor 50 not being able to rotate efficiently, resulting in a decrease in the flux linkage.

[0028] In actual manufacturing of magnet 56, dimensional tolerances may occur, for example, in the cutting process of magnet 56. It is known that the dimensional tolerance of the cutting process for thickness t is approximately ±0.05 mm, and the dimensional tolerance of the cutting process for width w is approximately ±0.07 mm. Therefore, the relationship between thickness t and width w of magnet 56 is calculated taking these dimensional tolerances into account. For example, assuming a situation in which magnet 56 is manufactured with t = 1.5 mm and w = 6.52 mm (t / w = 0.23), taking the dimensional tolerances into account, the minimum value of t / w is the ratio of the minimum value of thickness t to the maximum value of width w, which is 1.45 / 6.59 = 0.22, and the maximum value of t / w is the ratio of the maximum value of thickness t to the minimum value of width w, which is 1.55 / 6.45 = 0.24. In other words, taking into account the dimensional tolerance of magnet 56, it can be said that the flux linkage can be maximized if the relationship t / w = 0.23 ± 0.01 is established between the thickness t and width w of the manufactured magnet 56.

[0029] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. Modifications of the above-described embodiments are listed below.

[0030] In the above-described embodiment, the cross section of the rotor core 54 has a substantially square shape. However, the cross section of the rotor core 54 may have another polygonal shape, such as a substantially octagonal shape. Furthermore, the cross section of the rotor core 54 may have, for example, a so-called concave polygonal shape.

[0031] Furthermore, in the above-described embodiment, the magnet 56 was positioned so that the widthwise center position P of the magnet 56 overlapped with the midpoint M of the side 54a, but the positions of the center position P and the midpoint M do not have to coincide.

[0032] The technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful. [Explanation of symbols]

[0033] 30: Stator 50:Rotor 52: Shaft 54: Rotor core 56: Magnet

Claims

1. a shaft having a rotation axis; a rotor core surrounding the shaft; four plate-shaped magnets arranged on the outer surface of the rotor core; a covering member that covers the rotor core and the magnet; Equipped with The magnet has a substantially rectangular cross section perpendicular to the rotation axis, The rotor core has a substantially polygonal cross section perpendicular to the rotation axis, the outer surface of the rotor core on which the magnets are arranged is a flat surface without any recesses, When the thickness of the magnet along the radial direction of the shaft is t and the width of the magnet along the circumferential direction of the shaft is w, the relationship t / w = 0.23 ± 0.01 is satisfied over substantially the entire width of the magnet. Rotor.

2. 2. The rotor of claim 1, the rotor core has a cross section perpendicular to the rotation axis that has at least a first pair of parallel sides and a second pair of parallel sides perpendicular to the first pair of sides, the magnets are disposed on outer surfaces of the first pair of sides and the second pair of sides, respectively; a rotor in which central positions of the four magnets in the width direction overlap with the midpoints of the first pair of sides and the midpoints of the second pair of sides, respectively.

Images